We have four Windows Servers running Apache 2.4.27 acting as load balancers for our application server cluster running Tomcat. Recently, we have started to experience a high number of crashes with the web servers. Within the Apache error log, we see the following:

Between the four web servers, we often see over a dozen such events during the day - sometimes more, sometimes less. In some cases Apache will crash after the child process was restarted only 5 minutes before. The number of crashes goes down significantly during the night and weekends, but it still happens. As far as we can tell, we have not made any major changes to the configuration recently.

We were able to get a core dump as one of them was crashing. The following are some pieces extracted from it:

Looking at the Windows Event Viewer, we see the modules "libaprutil-1" and "libapr-1" as the faulting modules when the crashes occur. On a rare occasion we will see "ntdll" and "libhttpd" as the faulting module.

We have tried to increase the thread stack size (based on similar reports online) but that didn't help. We've enabled forensic logging, trying to determine if there was some sort of rogue request that could be knocking us over, but nothing seemed really out of place.

Is there something we can do to alleviate this issue or is this a bug within Apache?

We are not using PHP or anything similar. Is there a way to know which, if any, module is causing the issue? It looks like the module mod_ssl is on the exception stack; is it fair to say that the SSL module is causing the problems?

We have not upgraded to the latest version of Apache yet. Since this is a production environment, we've been hesitant to upgrade especially since the release notes don't give any indication that it solved something along this issue. Additionally, we've been running the same version of Apache for a while now in production, but these issues only started becoming a major issue in the last few weeks.